Echoes and Airwaves
by PurpleMoon3
Summary: Clairestiel hasn't quite managed to get off the crazy train, and Loki doesn't know why the he suddenly has a sister but he's not complaining. Friendship. Always-Vessel-Claire becomes the incarnation of the Tesseract and Loki comes along for the ride.
1. Chapter 1

**Echoes and Airwaves**

**A Supernatural/Avengers Crossover**

**Post _Avengers_, Post _Supernatural_ S7:23.**

"No, I'm perfectly sane. But then, ninety-four percent of psychotics think they're perfectly sane. So I guess we have to ask ourselves; what is sane?" - Castiel, 8.2

"The sky bleeds, the ground quakes. It's cosmic. No demon can swing that. Not Lilith, not anybody." - Ruby, 4.1

* * *

Loki had lost. His army lay dead, his person violated by a dull-witted berserker, and once again Thor was victorious and being lauded by the masses. It a little depressing, but at least he'd wrought significant enough damage that sweeping his actions away as mere 'tricks' would be impossible. 'Twas not Mischief, but Mayhem as his ever-growing body count continued to rise with every corpse dug out of the war zone.

For sickly shining moment, Loki wondered if he would have made Laufey proud in a way that Odin never was.

_But I don't have a Father. None that would claim me, or I them._

Thor's expression was stony, as they entered the park. Surrounded by flowering trees and birdsong, chattering rodents, it was hard to imagine that just beyond the lines lay the bloated bodies of the Chitauri's living transports. Loki rolled his eyes as Asgard's heir apparent shoved Stark and Banner's pathetic little capsule -as rushed and _ad hoc_ as it had been Selvig's remained superior- at him. Loki took the handle and felt the fluctuating energies of the Tesseract flicker against the damping effect of the manacles.

_…fluctuating?_ Loki forced his thoughts from his own failures and probable execution to the cube of cosmic energies. Every few seconds a ripple would pulse over the multidimensional surfaces, and the pulses were increasing in a not unfamiliar frequency.

Loki's eyes flicked to the one who once would have claimed to be his brother, to tell him, _Wait, something is wrong_ but the muzzle prevented all sound, any whispered seidr, from leaving his mouth. Thor turned the handle on the Midgardian contraption, forcing the Tesseract's hand.

* * *

Everywhere.

They were _everywhere_. Dropping out of the sky like possessed comets, the legions of Leviathan circled with taunts, teeth sharp and wide and hungry. Theses were not those that died, but those locked away by Father. More physical than any werewolf, vampire, or naga that had died and awoken in Purgatory, after millions upon _billions_ of years in isolation, feeding and breeding on each other they Hungered. And Castiel's human vessel was just physical enough to _eat_, with Grace leaking from the many cuts and bruises from a year of almost non-stop battle like an invitation to an all-you-can-eat-buffet.

"Oooooh." A voice like a snake called as Castiel skidded to a stop at a small cliff. "Itsy-bitsy angel fell down the mountainside. Down came the Leeeeevis and ate the angel out! Up came the sun, and dried up all the blood… and then all the Levi's ate the Cass again!"

Blue-grey eyes peered over the edge to see several gaping mouths ready and waiting.

"We missed you, sweet thang." Another said, an impossible southern drawl stretched as his jaw unhinged to reveal row upon row of sharp teeth. "Not nice, to dine and dash like that… after all we did for _you_… little sister."

Dean was gone, hopefully had made it through the portal and back to earth. Castiel had successfully lured the Leviathans away from him. She'd done her best. She was tired. More were coming.

A big-mouth lunged, but Castiel was small and quick and ducked under and between his legs. She took advantage of the brief cessation of aerial bombardment and spread her wings.

Navigating Purgatory was nothing like traveling the heavens, or even transporting her vessel around earth. It was like being a boat at sea during a storm, and the tumultuous waters were made even worse by the many enemies that shot through her flight path like cannonballs of entropy.

"_You're going to die._" Lucifer's voice echoed through the non-corporeal plane, the near sentient madness using Castiel's panic as a foothold. "_Again. Do you think Daddy will bother bringing you back? I mean, you just keep fucking up. Third time was clearly not the charm._"

Castiel stumbled, splashing into a stream, and glared at the shade. "Shut. Up."

_"Why? You can't get out. You're stuck here. Dean *left* you behind. Dropped like a hot potato. Might as well give up. Let 'um eat ya. Might be quick! Sammy's head was sooo much more interesting."_

Castiel shook her head, shivering even as taken memories of her skin roasting off her skeleton became so strong she could smell the pork. She trudged toward the bank, water-logged coat dragging her down.

"Hello." A pair of cold, clammy hands wrapped around her ankles. Castiel had just enough time to identify the elongated head as belonging to a Kelpie before the aquatic equine pulled her deep. Castiel twisted, bubbles flying from her mouth as the monster expertly wrestled the small angel and tied her in her own clothing. Dull teeth bit down, breaking bone, and in a desperate move Cas shifted back to the other plane. Her clothing ripped, and her wings tore under the force of the starved Kelpie's rage at her prey slipping form her fingers.

Buffeted by Purgatory's gale, Castiel flew. Leviathans snapped up her scent. Harpies screeched at her passage. Hostiles were Everywhere. This was to be her existence, for as long as that existence continued.

Maybe it was a punishment for trying to take Father's place.

She'd failed. Whatever the test had been, Castiel had failed it.

Had she been corporeal and not mid-flight, the wail that escaped Castiel's mouth would have shattered glass and cracked earth.

Lucifer was at her ear. "_Blasphemer. Traitor. Kinslayer._"

Castiel's grace flagged. She would need to reform soon, or risk permanent damage to her vessel, and the Leviathans were catching up…

Something like Grace flickered ahead. It was dim, hidden in a high tree -but Castiel had heard rumors, before, or portals that lead from Purgatory to Hell if one was of a mind to find them- but there was a certain dulled familiarity to the energy wavelength. It felt like home.

Could there be another angel here, hiding?

_"Going to kill him, too?_" Lucifer asked, curious.

"No." Castiel whispered, girl-small fingers reaching for that shining, flickering blue light that grew more familiar the closer she came. She knew who it was. Dean said he'd died. "But maybe he'll kill me."

Castiel screamed as the blue swallowed her, pushing from one plane to the next like meat going through a grinder.

* * *

Loki hadn't quite expected the reception that waited for them. No doubt Heimdall had alerted Odin that Thor was returning, for once the two rematerialized on the still-broken BiFrost an entire contingent of guards awaited them. Waiting on a pedestal were even more shackles, a collar with matching manacles for hands and feet. It was a compliment; the best he ever received.

Some did battle, others did tricks.

Loki did both and thus he was doubly dangerous.

And it seemed that Odin, at least, could recognize the warning signs the Tesseract was giving off. His good eye crinkled as the guards stepped forward to take Loki from the Thunderer and put the newly made chains in place, but as he rushed forward the ceremony was disrupted.

"Thor, quickly, give me the Tessa-"

Too late, the Cube shone like a small sun, and with a roar energy exploded outward knocking everyone off their feet. It was only by hastily grabbing the handle of Thor's immovable hammer that Loki wasn't blasted _back_ into the Void, this time without access to magic to save him. Several of the decorative soldiers Odin had brought out were themselves cast into the Black, unable to keep their footing.

"By the nine-!"

The Tessaract as it had been was no more. Surrounded by the remains of the Midgardian device and shards of dying Cube was a naked girl-child. She was wet as though covered in birthing fluids, and battered wings of energy fluttered in and out of sight at her back. Tired eyes glowed with the cerulean, cosmic power of the now missing Tessaract. Selvig _had_ referred to the thing as a _her_. Her blonde head turned, birdlike, taking in Asgard and her people.

She froze when she saw him, confused face blanking. What left her lips was a whisper, but in the silence left by her entrance all could hear the word, "Brother?"

Loki didn't know why she said it, but he could see the way she looked at his chains, his muzzle, at the armored and bristling warriors around them.

Her next word was spit as she stood on colt-like shaking legs. "Pagans."

That little chest heaved as Odin slowly advanced on the girl, eye narrowed as energy gathered around the King's hand. The girl's expression remained composed, but then she spun on her heal and ran. And crashed into Loki, wrapping her arms around his waist and sending them both over the edge…

Loki's blood rushed in his ears.

_ Not again, no, no, not again please….!_

* * *

"No!" Thor yelled, grasping at air as his brother and the girl disappeared over the edge of the not-yet-rebuilt BiFrost like he did in so many nightmares. "Loki!"

Thor watched, disbelief and despair thick, his Father once again at his side as they watched Loki fall… but then portal-like energy crackled, and Loki _vanished_. The strange girl that looked upon the Trickster with wonder and called him _brother_ with him.


	2. Chapter 2

**Echoes and Airwaves**

**A Supernatural/Avengers Crossover**

_"You got a trickster on your hands." - Bobby, 2.15_

_"He has disobeyed his king… his fate is in his own hands now." - Odin_

* * *

They were falling through darkness, but the pinpricks of light in the sky and the single shining moon suffused the air with a comforting, non-Void glow. The iron like grip on his torso loosened as they dropped. Loki twisted, desperately trying to orient himself before man and child slammed into the midnight ocean like a bird crashing into a sparkling window.

It was a softer landing than hard earth, but not by much. Worse yet, dear Thor's muzzle and manacles were still in place and weighing him down. Loki kicked for the surface, eyes stinging from the salt, and watched as the girl drifted away from him. Arcs of dying energy followed the small body into the abyss. It was incredibly difficult to swim without the full use of his arms, even discounting the added difficulty of the incredibly dense iron alloy sinking his magic and his arms.

The glow had left her eyes. Loki's lungs fluttered in his chest, desperate, but the burn was nothing compared to what he had been trapped in before the Chitauri found him. She was sinking. Unless they'd come down close to land, it wouldn't matter if he reached the surface or not. One could only tread water so long before everything gave out and the soft, soft black-blue lulled one to sleep where pressure crushed all your worries away.

He didn't even have the magic to save himself.

Loki shot a jet of bubbles out his nose and turned himself around, pointing with his arms and kicking hard. He used the added weight of the chains to his advantage, searching out the last spot he'd seen a flash of light. If he looked up - and suddenly he couldn't be sure it was up, the light was far the darkness was everywhere- and his eyes hurt and his head throbbed and his chest burned…

His fingers touched a stringy strand in the dark. He put on a burst of energy and caught a fist-full of hair, jerking the body toward him. She was cold, clammy, the faint pulse of blood under his fingers the only sign of life. Loki's stomach curdled. They were so deep he couldn't see the moon anymore, and they were steadily sinking deeper.

He had no magic. He was-

_I have me. As always. There is _**me.**

-clutching the girl impossibly tight, hoping his half assed plan would work. Loki turned inward, beyond what Thor's chains would leech away. No time for illusions and fantasy. There was only cold, hard truth. The water practically freezing.

Unseen in the dark, Loki's skin lost all warmth as the water around them hardened and gradually carried the two upward.

* * *

Castiel is drifting. Angels have no need of sleep, but Castiel knows what it is to be human, to be utterly exhausted, and she gives in to the soft drifting between awareness and true unconsciousness. All sensations are somewhat dulled when wearing a vessel, grace coating and suffusing human nerve endings like a sheath of velvet steel, and the frigid waters of the Pacific made a serviceable enough bed.

The last time she'd passed through she's been looking for God, but Dean's necklace never warmed in her hands and all that was left was a lonely despair as her disobedience barred her from her brothers and sisters in arms. She'd still prayed, then.

_What am I supposed to do? _

Perhaps falling, sinking to the bottom would be best. Then she wouldn't be at risk for messing up so fantastically. She was -before everything else- a soldier, a weapon to be pointed; that was what she had been shaped into existence for… she wasn't Heaven's Sheriff or Father's Heir. That had been Lucifer's sin, hubris, and now hers as well.

_Jesus wept._

_"Maybe." _ An unwanted faint voice echoed out from the back of her mind. "_Maybe Father keeps bringing you back because he doesn't want you with him. Exile for Eternity. Doesn't it burn…?"_

There was a cradle of cold around her. Lucifer gave an annoyed huff as the comfort drowned out the tangled memories of hook and hot irons and too many brothers and sisters falling to the warped remains of souls just to give her time to get out. Forty years.

"You're crying…"

Between one sluggish thought and the next, Castiel came to full awareness and the sight of Sol setting over the horizon. She was lay propped between her brother's sprawled legs. Red eyes, but not the opaque film of a demon, watched her wonderingly. A periwinkle finger trailed along her cheek, frosting wet droplets with its passage and gathering one drop on the tip. He raised the diamond like tear to the dying light, then smirked and tucked it beneath crackling leather. He smiled down at her, a certain smarminess that was achingly, painfully -her brother had not been cruel when she'd been mucking up his game with the Winchesters, but he had not been _kind_ either- familiar.

Why was he always assuming strange faces? Couldn't he be content with one?

The finger was back, absently tapping her nose. "Hmm. Now what I am to do with you, my dear Tessa?"

Castiel uncrossed her eyes, nose wrinkling as she focused on the decidedly not angelic iris' above her. An unsettling idea skittered along her spine. "My name, is Cas-" _-tiel._ Could she claim such, after everything she'd done? "Cas. My name is Cas. Not Tessa."

"Is that so?"

"Yes."

She shook herself and reached up, ignoring the aborted movement to flee as she took his face in her hands. Blue bored into red, and the niggling worm of an unhappy thought danced into the fore. She could see pain, and regret, and rage that would give Lucifer a second thought… but instead of a renegade angel hiding beneath layers of mythos and enchantment there was only the faintest of echoes… like holding an old conch shell and hearing the ocean it had once been a part of.

_Anna._

Chain clinking, her brother gripped her wrists and gently tried to lower them. Castiel dropped her arms to her lap, head bowed. Her mind grew pleasantly blank. "You don't remember me, do you?"

This time the smile was brittle, the eyes wary. "Let's try this again." Her brother spoke, voice pitched oddly. "I am Loki. And you're Cas. It is a pleasure to meet you."

He raised her hand to his lips; dropped a light kiss on them. Involuntarily, she blushed. _Of course. You never really change, do you brother?_

Grace sparked inside her, yawning like a cat, and the thought of how much stronger she'd now become -strong enough to be Raphael's equal despite the suspicious lack of ill-gotten souls- and as she squeezed her hand her own blade filled her empty palm. Loki stiffened before curling forward, curious.

"Is that? It is! An Uru blade…"

Eyes narrowed in concentration, Castiel set blade to shackle and slowly, carefully, began to saw.

They both ignored the sparks pockmarking their skin.


	3. Chapter 3

**Echoes and Airwaves**

**A Supernatural/Avengers Fanfic**

"So what, you're like a Delorean without enough plutonium?" - Dean, 5.13

"The insanity of the plan is of no consequence."- Dr. Zola, _Captain America: The First Avenger._

* * *

Loki, invisible but still very present with the aching ribs to prove it, watched the mortals of Manhattan go about their day as thought he had never summoned forth a horde of blood-starved Chitauri from the Tormented Space. He'd expected more of what he left behind, perhaps enough improvement to have bodies of his useless army cleared away, but there was not a single sign of the war he'd brought to them… though there were signs of _a_ war. It was hard to miss all the propaganda cleverly hidden about, bright posters standing in contrast to the grimy streets and forced cheer: _Food is a Weapon, Don't Waste It._ Several images proclaimed the virtues of gardening, and one Loki found particularly memorable depicted a man riding with a ghost the fallen prince could only assume was the much hated Hitler.

The Trickster walked through the early morning streets at a leisurely pace, carefully avoiding the streams of humanity as he adjusted his clothing to match the times. Truthfully, there wasn't much that needed changing as a good fitted suit was always a good fitted suit, and the Midgard that the Tesseract had brought them back to wasn't so far back in development that brightly colored puffballs and cod-pieces was the height of respectability. Loki wandered up to a young boy with a stack of thin papers under his arm hawking his wears. The child's trousers were fraying at the bottom, but for all the shabbiness plump rosy cheeks said someone looked after him.

Smiling, Loki banished his concealment spell and waited. The boy held his paper, shouting at some woman with her hair tied tight under a kerchief, and sighed when she shook her head and walked on. He turned, and promptly fell backward onto his ass with a cry of surprise. The surprise quickly gave way to a wide, cheeky grin and an offering of newspaper.

"Sir! Ah, sorry, didn't see you there! We got the _Hun _on the _Run_!" The headline was prominent.

Loki took the paper and flicked a nickel at the boy, who expertly caught the coin and dismissed the rude gentleman with barely a thought. Loki wondered how long, if at all, it would take someone to notice that there was a nineteen ninety-four coin circulating in -Loki glanced at the paper for confirmation- nineteen forty-four.

Smiling, Loki tucked the paper under his arm and continued on his walk, mind racing. Sixty-eight years into the past. Even with the Tesseract at his disposal Loki had thought, had known in a way that all sorcerers knew, swimming against the flows of time was a dangerous and nearly impossible thing. Only the Time Gem was capable of allowing the user to travel to the past without causing a self-annihilating paradox, but that treasure had been lost to, well, _time_. The only Infinity Gem with a known location was the Power Gem kept with the Gauntlet in Asgard's vaults.

_Correction. In Approximately seventy years time Odin shall have Soul Gem as well, delivered unto him by his unwitting son. And the Titian still has possession of the Mind Gem, though I at least am free of its influence… which leaves the remaining three still unaccounted for. Space, Reality, and Time…_

A bell jingled above Loki's head. He removed his fedora and looked expectantly to the smiling waitress at the bar.

"Good morning!" Her cheeks flushed and Loki turned up the charm, complimenting hair that must have taken hours to curl. Loki hopped onto a cushioned bar stool and brushed his fingers against hers as she handed him a wrinkled menu. Several things seemed to have been taken off in recent times. A glass of water tapped the wood in front of him.

"If it pleases you, I'd like some Pancakes."

"It would please me greatly." She playfully responded, "Would you like anything to drink? I'm afraid syrups and honey are by request only with extra charge. We do however has excellent strawberry jam, local. The boss' wife is very proud of it. The coffee is a bit weak right now, what with the war and all, but our tea is excellent."

"Tea then, and the jam."

"Okie-dokie!" She left, heels clicking, and Loki tuned out the shout to the kitchen. Instead he flipped open the paper and scanned the articles with half an eye. Actual information sprinkled between great clumps of propaganda, the usual advertisements, and on page two a very prominent gray-scale splash of what should have been red, white, and blue.

_Now who's the man out of time?_

"Of course…" Loki mused, twirling a fork into a pen, and began to sketch out ideas. Seventy years. Seventy years with no Other standing over his shoulder. Seventy years with no Heimdall waiting for the second prince to show vulnerability. Seventy years of _true_ freedom. To plot. To plan. To prepare.

"Hey, Mister? You alright?" The woman asked as she returned with his meal. When had he started laughing?

Loki covered his dying chuckles with a hand and shook his head. "I-I'm fine. Just had a thought."

She rested her elbows on the bar, grinning back. "Care to share? I could use a laugh myself, and so could Ern. Isn't that right, Ern!"

There was a sound that could be taken for agreement from the back.

"Well then," Loki slathered the homemade jam over his pancakes and took a bite, relishing the taste. "How about a story? There was once a man, called Donnar, who possessed a magical hammer, though through the scheming a clever giant did not possess it for long…"

* * *

Loki didn't bother with the door when he returned from his reconnoitering; not that the Tesseract seemed to take particular notice of the trickster's sudden appearance. A section of carpet had been ripped up to reveal smooth cement underneath. The little girl sat beside the hole with a bowl of beaten bronze and chalky hand prints staining the bright green of her dress.

Loki had picked out the dress. It was a brighter, lighter shade than his own color but went nicely with her hair and the blue stitching softened the glow of her eyes. If not for the coat that had come from who-knows-where, she would have looked like an adorable dream in sheep-skin boots. Loki sniffed at the burnt remains in the bowl. Myrrh. He prodded at a tan coat sleeve. "What's this?"

The blonde paused in the act of lighting candles. "Claire's."

Loki's lips thinned at the unsatisfactory answer. He had asked, very nicely, for her to stay in the room, but from the ritualized set up his request had not been heeded. If he remembered his Midgardian History, there were yet certain unsavory individuals on planet with the capabilities to find and track his self-proclaimed sister. "Who is Claire?"

Cas' face blanked, and she pointedly ignored the question. Instead she stood and patted her hands clean on her dress, before a glare and blink restored the material to its original pristine state. Loki wondered how well that trick worked with blood stains.

"Zo-da, Ka-Ra." Uru sliced skin, and Loki felt his heart jump as thick red blood dripped into the bowl. It moved independently of gravity, circling the sides as power began to build and pulsing blue spider-webs began to crawl up Cas' skin as though tracing her veins. "Zo-da, Mo-Ka-Ra-"

"What are you doing!?" Loki yelled as the room began the shake. He lunged forward, grasping the chanting child by the shoulder and shaking hard. Her sword fell the ground, disrupting the chalked design and dispersing the energy with a sizzle.

"Bringing us here was a mistake! I was sending us home!" Child-wide eyes darted to an empty corner, and she looked on the verge of tears. Loki breathed out through his nose. What was home? What did _she_ know of home? "The longer we wait to return, the harder it is to do so. Compound that with how far back we've gone… I was barely able to get Sam and Dean back from eighteen sixty-one, and that was a controlled jump _with_ an anchor, if we don't go soon..."

Loki stored away the names Sam and Dean along with Claire. SHIELD technicians, perhaps? But SHIELD hadn't gotten very far with their experiments, unless it was something off the books, but then if the Tesseract could warp time and space and assume a humanoid form who's to say what it, she, could and couldn't do?

He ran his fingers through her hair, scratching at her scalp and until the tension melted from her shoulders. "Little sister, I do not _want_ to go back."

"…I do not understand."

He tapped her nose. It seemed to annoy her like nothing else did, and she was always so cute when her eyes crossed to track his finger. Going back would be more problematic than helpful. He had time, and he had a Tesseract with more applications than Odin and all of Asgard ever dreamed. If the AllFather had known, surely he wouldn't have left her…

"There is," How much should he reveal? How much did she need to know? Could he use her power without her consent? Seventy years… "I am not a nice man, Cas. I have enemies that have promised to make me wish for something as sweet as pain. I am in no rush to return to them."

Her eyes wandered back to the empty corner, her little hand squeezing his leg as if staking claim. "No. I would not be, either." She laughed, suddenly, high and girlish. "All the torture, twice the self-righteousness!"

"You've been tortured?" He pried her fingers from his knee, instead threading them through his own.

Those baby-blue eyes were suddenly very, very old on her small frame. "They called it persuasion."

* * *

Note: In case it wasn't very clear, because I only just kinda mentioned it, Cas gave Loki the sigils on his bones to hide him from angels. This was done mostly because Cas is paranoid and thinks Heaven might send assassins after Loki like they did Anna, and incidentally the magic squiggles also prevents Heimdall from using his mojo to find Loki.


End file.
